Port knocking is an authentication technique that utilizes a pre-determined sequence of closed port connection attempts to specific Internet Protocol (“IP”) addresses. This sequence is known in the art as a knock sequence. Port knocking utilizes a daemon that monitors firewall logs for the correct knock sequence. Port knocking essentially provides a dynamic configuration of a default drop firewall policy to allow temporary connections from authorized sources after an authentication request.
Single packet authorization (“SPA”) is a next generation variation of port knocking technology. SPA allows a single “knock” implementation in which the knock consists of an encrypted packet that is captured passively by a SPA service. The SPA service validates the encrypted packet to allow temporary connections from authorized sources.